1. Field of the Invention
This invention is related in general to the field of computer systems. In particular, the invention consists of a copying technique where data at a primary storage system is backed-up to a secondary storage system.
2. Description of the Prior Art
Computer storage systems such as storage servers commonly employ backup techniques utilizing a primary storage system and a secondary storage system to maintain a redundant copy of stored data. The secondary storage system is typically located at a location that is remote from the primary storage system and receives data from the primary via a high-speed data link such as an optical-fiber connection. In other cases, the secondary and primary storage systems may physically reside within the same storage server and data is backed up locally. Tracks are arbitrary units of storage such as a partition, a hard-drive, a tape, or an array of disk-drives that can be formatted to contain a set of sequentially addressed data records. Data transfers between storage systems often take the form of either single-track transfers or multi-track transfers.
One form of remote redundant storage is peer-to-peer remote copying (“PPRC”) over fiber-optic cable (“fibre”) using multiple communications channels. Each communication channel is formed using a port from the primary storage server routed to a port of the secondary storage server through a bridge, bus, or network switch. Each port is analogous to a network interface card in a local-area network system (“LAN”). The primary and secondary storage servers may have a multitude of ports and the actual communication paths are determined by the routing devices.
Performance of a PPRC system is maximized when the primary ports are driven to saturation, i.e., 100% utilization of port bandwidth. Requests to send information from the primary to the secondary storage server are usually assigned a priority level. During periods of high bandwidth demand, low-priority requests should are sometimes throttled to ensure efficient execution of high-priority requests. A device implementing a port-request control algorithm is required to efficiently manage these communication channels. It is desirable that this control algorithm be responsive to all data-transfer requests, ensure execution of high-priority tasks, and optimize the bandwidth utilization of the communication channels.
In U.S. Pat. No. 5,881,050, Denis Chevalier et. al. disclose a method and system for non-disruptively assigning link bandwidth to a user in a high-speed digital network. Link bandwidth is assigned to requesting users based on predefined connection priorities. A predefined reservable link bandwidth is divided into nominal bandwidth portions and common bandwidth portions, both of which are assignable on a priority basis.
An important aspect of Chevalier's invention is that common bandwidth is associated with and subservient to nominal bandwidth, thus preventing disruption of established network connections. However, Chevalier does not address balancing the priority of the work load over the communication channels. Accordingly, it would be advantageous to utilize a control algorithm to simultaneously balance the work load and task prioritization across the data paths while maintaining a relatively uniform bandwidth utilization.